The present invention is generally directed to a plunger type electromagnetic hammer for use with printers using type indicia and, in particular to a hammer structure for use in an electromagnetic hammer assembly wherein the plunger and head portions of the electromagnetic hammer are made of the same electromagnetic material.
Reference is made to FIG. 1 wherein a hammer assembly of the electromagnetic hammer type according to the prior art is shown. The plunger and head portions are made of the same electromagnetic material because of cost and size restrictions. The prior art hammer consists of a plunger portion 101 and a head portion 103 at the leading end of plunger portion 101, the head portion 103 being the same size as a type element. The radial distance Y' between the portion 103 and yoke member 104 is smaller than the longitudinal distance X' from the magnetism introducing face 117 of plunger 101 to the end of a coil 109 in yoke 104.
The result of this configuration is that magnetic leakage occurs at the portion of head portion 103 near plunger portion 101. This reduces the magnetic flux available to thrust plunger portion 101 in the direction of arrow 120. Because of the magnetic leakage, the efficiency of the hammer is lowered and the heat released is increased. In addition, the hammer in accordance with the prior art cannot respond at high frequency levels and desired impact energies are not generated.
Accordingly, there is a need for a print hammer in which the efficiency of the magnetic circuit of the electromagnetic hammer assembly is enhanced to insure a high frequency response at a low power consumption with a high impact energy.